DONGGUAN, China, Nov 3, 2012 (AFP) - The Englishman's 11-birdie blitz put him at 18-under-par 198 through three rounds, level with overnight leader Oosthuizen who battled to a 70 on the par-72 Olazabal Course at southern China's Mission Hills.
On a day of red numbers at Dongguan, even Westwood's brilliant round was eclipsed by America's Brandt Snedeker, who shot a course-record 60 -- and only narrowly missed a birdie putt on 18 for a magical score of 59.
Westwood and Oosthuizen will go into the last round three strokes ahead of America's Phil Mickelson, a double WGC-HSBC Champions winner and four-time Major champion, who blazed back into contention with a 66.
Ian Poulter and Bill Haas were four shots off the lead along with Ernie Els, who whittled down fellow South African Oosthuizen's overnight advantage before imploding with a watery double-bogey on the par-five 15th.
Snedeker was five off the pace after his astonishing 60, which was all but matched by Westwood as the former world number one started the day nine shots adrift and finished with the joint lead.
"I just wanted to come out fast and try to get some momentum. That's been missing from my game the last couple of weeks," said Westwood.
"I came out as quick as you like with three birdies, and that got me going and the hole started to look bigger."
Snedeker was playing in the day's first group after modest rounds of 72 and 71, but he quickly set the course alight with four birdies through his first four holes before turning at six under.
Another birdie on 10 was followed by a "fluke", 75-foot birdie on the par-three 13th. Snedeker went eagle, birdie on 15 and 16, and then rolled in a 25-footer on 17 to raise hopes of a magical 59 -- but his birdie putt on 18 crept just wide.
"I'd love to have that putt again," he said. "I hit a great putt and it stinks not doing it (59) but it's still a great round and I got back in the golf tournament, which is nice."
With Oosthuizen and Els locked in a dogfight in the final group, Westwood was tearing up the course as he played alongside his Ryder Cup team-mates Poulter and Martin Kaymer, the defending champion.
His triple-birdie start was followed by three more by the halfway mark, another on 11 and then four in a row from 14 to 17, aided by a red-hot putter.
"The course is in great condition and we're starting to get used to playing it," said Westwood, when asked to explain the day's low scores.
"As the week's gone on and we've played it and walked it, we're starting to see lower and lower scores."
Oosthuizen, the 2010 British Open winner, had shot 63 on Friday to go 16 under after two rounds, a World Golf Championships record. But he found day three heavy going in the company of his mentor, Els, and Adam Scott.
The 30-year-old paid for a slow start when Els caught him at the top of the leaderboard on the 14th hole. However, the veteran Els immediately dropped back when he splashed into the lake on 15 for double-bogey, and also bogeyed 16.
Oosthuizen went close with an eagle attempt on 15 but it was typical of a day in which his putts just wouldn't drop.
"Frustrating," he said afterwards. "Early I didn't play well and then started to find a little bit of form on the back nine, but just didn't make any putts.
"You can see all the birdies that were out there, looking at the leaderboard. But I'm still in a good position going into tomorrow."
Northern Ireland's Graeme McDowell recovered from slamming his hand in his hotel door to shoot a 68, while India's Gaganjeet Bhullar also got among the birdies with a bogey-free 63.
Leading third-round scores at the $7 million WGC-HSBC Champions on the Olazabal Course (par-72) at Mission Hills in southern China on Saturday:
198 - Lee Westwood (ENG) 70-67-61, Louis Oosthuizen (RSA) 65-63-70
201 - Phil Mickelson (USA) 66-69-66
202 - Ernie Els (RSA) 70-63-69, Ian Poulter (ENG) 69-68-65, Bill Haas (USA) 69-67-66
203 - Brandt Snedeker (USA) 72-71-60
204 - Adam Scott (AUS) 65-68-71, Martin Kaymer (GER) 68-69-67, Gaganjeet Bhullar (IND) 73-68-63, Scott Piercy (USA) 68-68-68, Carl Pettersson (SWE) 70-68-66
205 - Jason Dufner (USA) 68-66-71, Luke Donald (ENG) 68-68-69
206 - Prom Meesawat (THA) 67-70-69, Shane Lowry (IRL) 66-68-72, Marc Leishman (AUS) 73-68-65, Thorbjorn Olesen (DEN) 71-65-70
207 - Hiroyuki Fujita (JPN) 73-67-67, Keegan Bradley (USA) 71-68-68, Bubba Watson (USA) 66-72-69, Gonzalo Fernandez-Castano (ESP) 71-67-69, Marcel Siem (GER) 71-70-66, Thongchai Jaidee (THA) 70-68-69
209 - Justin Rose (ENG) 72-70-67, Wu Ashun (CHN) 68-70-71
Selected:
210 - Peter Hanson (SWE) 66-71-73
214 - Graeme McDowell (NIR) 71-75-68
217 - Francesco Molinari (ITA) 74-69-74, Nicolas Colsaerts (BEL) 73-73-71